Alzheimer's disease is a complex, multifactorial syndrome characterized clinically by early learning and memory deficits that progress into a severe and as-of-yet irreversible dementia. The vast majority of cases occur sporadically, and age and genetics are the strongest risk factors for onset. The APOE gene is the most strongly associated with the development and clinical progression of sporadic AD. The molecular dynamics of APOE are complex due to differential effects of allelic isoform and synthesis and secretion by multiple cell types. To unravel this complexity, our laboratory has generated induced pluripotent stem cells from patients with sporadic AD. Though the majority of APOE in the brain is produced by astrocytes, previous findings from our lab demonstrated an association of APOE genotype with AD-relevant phenotypes in human basal forebrain cholinergic neurons - a cell population which dies early in AD. Limited information is available about the role of neuronal APOE in neurodegenerative change. This proposal will therefore test the hypothesis that APOE isoform exerts cell autonomous effects in cholinergic neurons that result in altered amyloid processing (Aim 1) and calcium homeostasis (Aim 2). Our findings in this novel human cellular model of genetic risk in sporadic AD will build upon insight from previous rodent and human clinical studies while providing unprecedented experimental control of gene isoform and cell type of expression. The proposed studies will clarify the multiple roles of APOE in human neural cells and identify critical intersections with proposed molecular mechanisms for AD. In doing so, we aim to develop strategies for earlier diagnosis and more successful intervention of this debilitating disease.